This invention generally relates to housings that hold a plurality of circuit packs and more specifically relates to housings that suppress radio frequency (RF) radiation generated by circuit packs contained therein.
Electronic circuit packs, also referred to as printed circuit boards, are widely used in various types of electronic equipment. Circuit packs typically support and connect electronic components including integrated circuits that operate as analog devices, digital devices, or RF components. The frequency of operation of the RF components continues to increase as technology permits higher frequencies of operation. Digital devices are also undergoing a similar evolution wherein clock speeds continue to increase, which is the equivalent of operating at higher frequencies. The tendency of components and conductors on the circuit packs to generate undesired RF radiation increases as the frequency of operation and clock speeds increase. The problem of undesired RF radiation is exacerbated by the desire to mount a plurality of circuit packs in relatively close proximity to each other in a cabinet in constructing complex electronic equipment. Excessive amounts of RF radiation from one circuit pack can adversely impact the operation of an adjacent circuit pack as well as causing undesired amounts of RF radiation to the external environment. It is difficult for the designers of circuit packs to substantially eliminate undesired RF radiation, especially where components on the circuit pack operate at higher frequencies or high clock speeds.
The design of enclosures for circuit pack is further complicated by the need to keep components on circuit packs from overheating. The amount of heat a component dissipates normally increases as the frequency of operation of the component increases. Thus, the need for additional cooling increases along with the undesired RF radiation levels with higher frequencies and clock rates.
A common design for an enclosure that houses a plurality of circuit packs uses a metal enclosure that surrounds the grouping of circuit packs that are plugged into a backplane that provides electrical connections to the circuit packs. The bottom and top planar walls of the metal enclosure are perforated to accommodate the flow of air generated by one or more fans. While such a design may be effective in minimizing undesired RF radiation to the external environment, undesired radiation among circuit packs in the enclosure is not effectively suppressed. RF radiation can create problems for a component on a circuit pack when the source of the radiation is another circuit pack and when the source of the radiation is another component on the same circuit pack. The internal reflection of RF radiation off walls of the enclosure can also cause problems. Therefore, there exists a need for an improved circuit pack enclosure that minimizes RF radiation problems inside as well as outside of the enclosure, while providing effective cooling for components on the circuit packs.
It is an object of the present invention to provide an enclosure that accommodates a plurality of circuit packs and minimizes RF radiation within the enclosure and to the external environment. A further object of the present invention is to provide effective cooling for components on the enclosed circuit packs while providing the improvement in minimizing RF radiation.
In accordance with an embodiment of the present invention, an enclosure includes spaced apart sidewalls and a bottom wall, rear wall, and top cover each forming an RF tight seal with the sidewalls, and defining separate chambers for a plurality of circuit packs. The edges of the sidewalls, bottom wall and top cover at the entrance to each chamber are configured to form an RF tight seal with the faceplate of an installed circuit pack. A connector engages the circuit pack and provides communication paths between the circuit pack and other equipment external to the enclosure. A fluid for cooling the circuit pack is input into each chamber and a means for allowing the fluid to escape is provided while being resistant to the transmission of RF energy. Surfaces of the sidewalls that are interior to each chamber are able to disrupt and absorb a substantial portion of the RF energy radiating from the enclosed circuit pack and thereby minimize the level of RF energy within the chamber.
In accordance with another embodiment of the present invention, a plurality of circuit packs each having an associated faceplate are used in combination with the above described chambers to form individual enclosures that provide RF isolation.